Many automotive vehicles are equipped with a pump to transfer pressurized fluid to a number of locations throughout the vehicle. Most of the vehicles in production today are equipped with one or more pumps driven by an internal combustion engine of the vehicle. Examples of such pumps include fuel pumps, water pumps, internal combustion engine oil pumps, transmission oil pumps, superchargers, turbochargers, power steering pumps, air conditioning system compressors as well as fluid pumps that provide power to actuation systems for devices such as automatic transmissions, transfer cases, clutches and a host of other vehicle pumping requirements. While many of these pumps have operated satisfactorily in the past, a few concerns exist.
For example, many pumps are configured as fixed displacement pumps to minimize cost of the assembly. The fixed displacement pump is typically sized to provide a maximum flow rate and pressure based on a peak demand of the system. During much of the vehicle operation, however, peak demand is not required. As such, the pump may inefficiently provide a relatively high output when a relatively low output is required. The energy associated with providing the higher output instead of the lower output may be viewed as energy waste.
Furthermore, some newer vehicle configurations, including hybrid vehicles, do not operate the internal combustion engine at all times. In particular, it is contemplated that a hybrid vehicle may be constructed to include an internal combustion engine and some other source of power such as a battery and an electric drive motor. To realize maximum fuel economy, the internal combustion engine of the hybrid vehicle may be turned off and turned on many times during vehicle operation. As such, it may be undesirable to have the internal combustion engine as the sole source of power to the fluid pumps.
Pumps driven by electric motors may also be used within motor vehicle applications. However, a pump solely powered by an electric motor typically does not provide the same efficiency of operation as a pump mechanically driven by the internal combustion engine. Accordingly, a need in the art may exist for a pump having a dual source of power to improve vehicle energy efficiency and provide pumped fluids during different modes of vehicle operation as necessary.